Hello, I'm Keith and happy to help you with your question.
Don't panic, it is not unknown for HMRC to make a mistake in these cases and get the amount wrong. Put it in the hands of your agent and tell them of your husband's condition. He or she can ask for an explanation of what and why they are on about. In any event a 1993 debt cannot almost certainly be enforced in Scotland. The relevant rule is:
The Prescription and Limitation (Scotland) Act 1973 applies in Scotland and provides for a time limit of 20 years for collection of debts.
However, debts that are not classed as tax, for example settlements, are subject to the standard rules of prescription (set out at schedule 1 of the 1973 Act) which prescribes a time limit of 5 years after the last effective action.'
You are doing the right thing consulting a solicitor, he will put your mind at rest and also put HMRC back in their box!
An immediate point that comes to mind is how the busines was operated, for example was it a company, if so it's probably a company debt and nothing to do with the individual?